This application claims the priority of European Patent Application No. 00 105 911.2, filed Mar. 22, 2000, the disclosure of which is incorporated herein by reference in its entirety.
The invention relates to water-soluble acrylic copolymers suitable as cement dispersing admixtures.
The quality of fresh concrete is determined by the ease and homogeneity with which it can be mixed, transported, compacted and finished. It can also be defined as the amount of internal work, necessary to achieve full compaction.
The Theological behavior of concrete is related to rheological terms such as plasticity and visco-elasticity of its cement paste.
Cement compositions, such as mortar or concrete, lose their flowability with the progression of time due to a fast stiffening effect caused by an early hydration reaction of cement and water. This loss of flow reduces its workability.
As the workability depends on the conditions of placement, the intended use will determine whether the concrete has the required workability.
Concrete from ready mix plants or mixed on job sites, used in civil engineering constructions, e.g. anchorage of big bridges, base plates or side walls and box culverts, in building structures such as heavy reinforced structures, concrete filling pipe structures or other complicated structures, demands to be fully compacted to achieve its required strength and durability. The existing and conventional method for compaction is by vibration of the freshly placed concrete.
A new production system for in situ-casted concrete is needed to improve significantly the cost situation as well as the health and safety aspects on the construction site.
Additionally, self compacting concrete leads to a higher productivity, shorter building times and to an improved labor environment.
Increased fluidity, defined e.g. as xe2x80x9cflow-table spreadxe2x80x9d, xe2x80x9cslumpxe2x80x9d and xe2x80x9cslump-flowxe2x80x9d, can be effected by using large dosages of water in the concrete, but it is well known that the resulting cement-based structure exhibits insufficient compactness due to excessive bleeding and segregation and consequently will have poor final compressive strength.
In order to avoid excess amount of water, flowing concrete can be produced by the addition of so called superplasticizers or high range water-reducing admixtures (HRWRs) like sulfonated melamine-formaldehyde polycondensates or naphthalene-formaldehyde polycondensates or ligninsulfonate based admixtures. All of these well known polymers are not capable of causing the treated cement compositions to retain high flowability over a sustained period of time (known as xe2x80x9cslump lifexe2x80x9d) without imparting a significant delay in the initial set time and considerable retardation of early strengths. An additional disadvantage is the inconstant and very low flow rate of freshly prepared concrete containing high quantities (e.g. 500 to 700 kg/m3) of cement and up to 20% of silica fume and fly ash, which flow rate cannot be improved by the use of conventional HRWRs.
For heavy reinforced fresh precast concrete it is desired that the cementitious mixture has sufficient fluidity to flow through and around the reinforcement steel-structure to fill out the mold and level off at the top of the mold.
In the past ten years various polymer-admixtures based on so called polycarboxylic acid salts, e.g. copolymers of acrylic acid with acrylic esters of polyalkylene glycols have been proposed for imparting high water reduction, high flow and prolonged slump life to concrete, but most of them do not lead to self compacting concrete without causing a too long retardation of the setting time and the early-strength development.
Enhancing early, i.e. 1 day, compressive strengths, is of high importance in the precast and prestressed concrete industry, and chemical accelerators such as tertiary alkanolamines, alkali metal and alkaline earth metal thiocyanates, nitrites and halides are known in the art for this purpose and can be added separately to the fresh concrete.
Since calcium chloride and other inorganic salts can initiate corrosion of reinforcing steel embedded in hardened concrete, tertiary alkanolamines which show both, accelerating and corrosion inhibiting properties are the most recommendable chemical accelerators.
Unfortunately, tertiary amines are well known to act as powerful catalysts for the cleavage of esters and from this reason cannot be premixed with the acrylic ester polymers of the art and stored over longer periods thus causing strongly reduced shelf life of the blend.
In order to improve the stability of such admixtures, a deactivated form of alkanolamines was demanded which is reactivated in an alkaline environment.
The problem to be solved by the present invention is, that conventional cement dispersing polymers cannot be used as admixtures to produce simultaneously high flow- and high strength selfcompacting concrete.
Said problem could be solved with the introduction of a super high flow- or self compacting concrete, which is or contains a multipurpose polymer simultaneously acting 1) as a HRWR, 2) as set- and strength accelerator and 3) as corrosion inhibitor, these problems could be solved, particularly the need for vibration can be significantly reduced.
Hence, it is a general object of the invention to providexe2x80x94as a result of extensive studiesxe2x80x94acrylic copolymers, which can solve this problem.
The invention is based on modified acrylic polymers having a) a poly (oxyalkylene) chain and b) a tertiary alkanolamine group which both are connected to the backbone of the polymer by ester bonds. Said polymers are obtainable by aqueous radicalic copolymerization of acrylic polyalkyleneglycol esters- and -amides with an acrylic acid and an acrylic ester of a tertiary alkanolamine.
In particular it was found that the relationship between the molar ratio of the free carboxylate groups to the polyoxyethylene ester groups and the polyoxyethylene amide groups in the polymer as well as the length of the polyoxyethylene chain strictly determines the performance of the copolymer as a dispersing, water reducing and slump-keeping agent.
The accelerating and anticorrosive effect of tertiary alkanolamines in aqueous solutions is known for long time. The inventive polymers react in alkaline cementitious compositions and the alkanolamine group is released from the polymer which is partly adsorbed to the cement surface. Due in particular to their close proximity to the cement surface, the released alkanolamines prove a high set accelerating and shrinkage reducing effect.
Moreover, results suppose, that the polymers also are adsorbed on the reinforcing steel bars in the fresh concrete where they can act as corrosion inhibitors directly on the surface of the steel.
A water-soluble acrylic copolymer with cement dispersing, set-accelerating and anticorrosive properties to steel, as well as an admixture comprising an amount of from 5 to 95% of said water soluble acrylic copolymer, are described.
Said polymer is obtainable by copolymerization of an xcex1,xcex2-olefinic monocarboxylic acid or its salt shown by formula 1 given below, a second acrylic monomer shown by formula 2 given below, optionally a third acrylic monomer shown by formula 3 given below, a fourth acrylic monomer shown by formula 4 given below and optionally a fifth acrylic monomer given by formula 5,
such that the molar ratio of constituent monomer units 1, 2, 3, 4, 5 is
a:b:c:d:e=(0.1-0.9):(0.01-0.80):(0-0.80):(0.001-0.3):(0-0.5)
and
a:(b+c+d+e)=0.1:0.9 to 0.9:0.1,
whereby
a designates the molar concentration range of constituent monomers 1,
b designates the molar concentration range of constituent monomers 2,
c designates the molar concentration range of constituent monomers 3,
d designates the molar concentration range of constituent monomers 4,
e designates the molar concentration range of constituent monomers 5
said monomers having the structural formulas shown below: 
wherein each R independently from each other represents a hydrogen atom or a methyl group,
R1 and R2 independently from each other represent a C1-C4-alkyl, a hydroxyethyl (CH2CH2 OH) group, an acetoxyethyl group (CH2 CH2OCOCH3) group, hydroxy-isopropyl (CH2xe2x80x94CHOHxe2x80x94CH3) group, an acetoxy-isopropyl (CH2xe2x80x94CHOCOCH3) group, or R1 and R 2may together with the nitrogen atom to which they are bound, form a morpholine ring;
R3 is a C1-C4-alkyl,
R4 and R5 independently represent an aliphatic, cycloaliphatic, araliphatic or aromatic or R4 and R5 may together with the nitrogen atom to which they are bond form a morpholine- or imidazole ring system,
M represents hydrogen, an alkali metal, an alkaline earth metal, an aluminum ion, an ammonium- or organic ammonium group, such as an ammonium group derived from alkylamines or alkanolamines, in particular amines comprising C1 to C4 alkyl and/or C1 to C4 alkanol groups,
x and y independently represent integers from 2-300.
In the solvent polymerization using an aqueous solvent, a water soluble polymerization initiator such as ammonium salts, alkali metal salts of a peroxy acid or hydrogen peroxide is used as the polymerization initiator.
Further, to control the molecular weight, a chain transfer agent such as alkali sulfite, hydrogensulfite, mercaptoethanol, thioglycolic acid or thioglycerol (3-mercapto-1,2-propanediol) may be used.
It is preferable that the inventive polymer has a number-average molecular weight of 1000 to 100000, still more preferably 1000 to 30000.
When the molecular weight is too large, the resulting copolymer will exhibit a poor dispersing effect, while, when it is too small, the resulting copolymer will exhibit not only poor dispersity but also a poor slump retaining effect. Moreover, a defined molar proportion of 1-5 to 1 of carboxylic-groups to methoxypolyalkyleneglykol ester side chains and methoxypolyalkyleneglycol amide side chains at the backbone of the copolymer is preferred.
The average molecular weight is determined by gel permeation chromatography using a set of defined polyalkyleneglycols as standard reference.
Following a further aspect of the present invention the inventive copolymers are employed for preparing a cement-dispersing, set accelerating admixture having shrinkage-reducing and anticorrosive properties to steel. Hence, further to the invention, said admixture preferably contains at least one defoaming and/or at least one air-controlling agent.
Still a further aspect of the present invention is a mortar, concrete, cement or cementitious binder containing the modified acrylic polymer according to the present invention in an amount of 0.01 to 10% by weight of the binder, said mortar or concrete having a unit content of binder composed of cement or a mixture of cement and latent hydraulic or inert microscopic powder of 150 to 800 kg/m3, preferably of 250 to 650 kg/m3.
In a preferred embodiment, the cement is Portland cement, white cement, high alumina cement, and cement blends wherein the latent hydraulic or inert microscopic powder is fly ash, slag, natural pozzolane, silica fume, burnt oil shale, metakaolin or calcium carbonate.
The inventive admixture can be used in liquid form, e.g. by addition of water, in powder form and can be added before, during or after the grinding operation of the cement or the cementitious binder.